1. Field of the Invention
The present invention relates to a method and an apparatus for tuning a finite impulse response (FIR) filter in an in-band full duplex transceiver.
2. Description of the Related Art
Today, most of the wireless communication systems have adopted a half duplex type. The half duplex type divides time or frequency to perform transmission or reception, thereby maintaining orthogonality between the transmission and reception. However, the half duplex type wastes resources (time or frequency).
An in-band full duplex (IFD) type has been suggested as a solution for solving inefficiency of the half duplex type. The in-band full duplex type is a technology of simultaneously performing transmission and reception in an in-band. The in-band full duplex type may theoretically increase link capacity up to twice, and therefore is an indispensable technology for achieving 1000 times traffic capacity required in 5G mobile communication.
However, the in-band full duplex (IFD) type has a problem in that a self-transmitted signal is introduced into a receiver and therefore the self-transmitted signal is very stronger than a valid received signal, such that the self-transmitted signal acts as a self-interference signal. For self-interference cancellation (SIC), there is an antenna region SIC technology of physically significantly spacing a transmitting antenna and a receiving antenna apart from each other. A technology for reducing a self-interference level using the antenna region SIC technology and canceling self-interference remaining in a digital region is in a commercialization stage. However, the technology is hardly applied to a small apparatus due to a physical space between the transmitting and receiving antennas.
For applying the in-band full duplex (IFD) type to the small apparatus, a technology for canceling self-interference in an analog circuit region without the help of the physical space between the antennas is required. As the SIC technology of the analog circuit region, there are largely a passive SIC technology and an active SIC technology. The passive SIC technology may use a passive element to easily obtain an SIC gain. However, the SIC gain is limited. Meanwhile, the active SIC technology may use an adaptive analog finite impulse response (FIR) filter circuit to obtain the SIC technology gain higher than that of the passive SIC technology. In this case, there is a problem in that the existing active SIC technology may not continuously maintain the high SIC gain while being quickly adapted to a change in surrounding environment over a wideband.